1. Field of the Invention
The present invention relates to a sealing structure and a method for sealing an electronic component, and more particularly, to a sealing structure and a method of sealing a surface mount type electronic component.
2. Description of the Related Art
A conventional electronic component known as a surface mount type electronic component, such as a piezoelectric oscillator, a piezoelectric filter, or the like, comprises a substrate having an electrode pattern disposed on an upper surface thereof, a cap and a piezoelectric element disposed in a space defined between the substrate and the cap. An electrode of the piezoelectric element is connected and bonded to the electrode pattern disposed on the substrate via a conductive adhesive. The cap is placed on the substrate to cover the piezoelectric element, and is bonded to the substrate by a sealing adhesive coated on the opening of the cap. The electrode pattern of the substrate extends outwardly from the bonded portion of the cap so that an extended portion of the electrode pattern serves as an external electrode to define a surface mount type electronic component.
In such a surface mount type electronic component, when mounting failure occurs after soldering and packaging with a printed substrate, corrective measures ranging from repair (removal) to re-soldering (manual soldering) are carried out in some cases. In re-soldering, a portion of the electronic component located near the electrode is manually heated by a soldering bit, but heat is transmitted to portions other than the electrode and creates a high-temperature portion. Generally, because a sealing adhesive is required to have flexibility, a resin adhesive having a relatively low glass transition temperature (Tg) is used. Transmission of heat having a temperature higher than the Tg of the sealing adhesive decreases adhesive strength of the sealing adhesive, and thus causes the problem of displacing or even removing the cap if an external force is applied.
To prevent this problem, a method using a sealing adhesive having a high Tg has been considered. However, a very high Tg is required, and such a sealing adhesive cannot provide other required physical properties, e.g., a desired expansion and contraction of a member in a heat shock test, thereby causing a problem of fracture, peeling or cracks. Although a high heat-resistant adhesive such as an inorganic adhesive can be used, such an adhesive cannot form a layer having a sufficient denseness to prevent penetration of a solvent during washing, and cannot provide and ensure good sealing properties.